Dragon soul

You will unlock this achievement/trophy from wandering around the vast world of skyrim, or if you play the main story. All you need to do is kill a dragon and the achievement/trophy will be unlocked

Dragon souls are required for unlocking each Word you find. After you slay a dragon, you automatically absorb its soul. You don't have to use them immediately, but activating a Word is an irreversible process. In order to unlock three words, you would need to slay three Dragons.